摘要:

AbstractX‐ray absorption spectroscopy studies are contributing both to the refinement of the geometry of metal sites already known from crystallographic studies and the elucidation of the coordination sphere in metal sites in metalloproteins where only limited information was available. Specific problems in the analysis of coordinating imidazoles can be overcome by applying multiple‐scattering simulations. The model for the lipoxygenase iron site derived from the EXAFS study, a coordination sphere predominated by imidazoles, may require some adjustment in view of the possibility of coordination by water, and has received independent confirmation from studies of amino acid sequence homologies and the interaction with catechols.The spectroscopy of lipoxygenase is not consistent with the presence of the organic cofactor, PQQ, nor with its coordination to iron, but would be consistent with the presence, but not the coordination to iron, of the carboxy‐hydroxy‐indoloquinone‐glutamic acid cofactor, CHIQG. From the observed amino acid sequence homologies it is concluded that plant lipoxygenases can be good models for the studies of mammalian lipo

ISSN:0165-0513    

DOI:10.1002/recl.19901090302

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractBasket‐shaped hosts were synthesized starting from the concave building block 4To this end, oligo(oxyethylene) bridges, containing different aromatic rings, were attached to the 3,6‐ and 3′,6′‐positions of the xylylene rings of4. These bridges include 5,6‐benzo‐1,4,7,10‐tetraoxadec‐5‐ene, 5,6,7‐benzo‐1,4,8,11‐tetraoxaundeca‐5,6‐diene, 5,6‐(2,3‐naphtho)‐1,4,7,10‐tetraoxa‐dec‐5‐ene, 8,9‐benzo‐1,4,7,10,13,16‐hexaoxahexadec‐8‐ene and 8,9‐(2,3‐naph‐tho)‐1,4,7,10,13,16‐hexaoxahexadec‐8‐ene chains. Alkali‐metal ions and protonated aliphatic or aromatic diamines are bound in these baskets in a 1:1 host/guest ratio. For the metal ions, a clamshel‐llike or a sandwich‐like complex is proposed. Aliphatic diammonium guests are bound in such a way that the methylene chains are wedged in between theo‐xylylene units of the host, as concluded from the upheld shifts observed in the1H NMR spectra of the guest CH2protons. Free energies of binding of the new hosts with nineteen guests were measured using the picrate extraction technique. The highest ‐ ΔG° values were obtained

ISSN:0165-0513    

DOI:10.1002/recl.19901090303

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe chromoionophoric behaviour of compound 1 in solution was studied in relation to the X‐ray structure of its complexes with Na+, Ba2+and Ag+. Interaction between the metal ion and the “soft” nitrogen atom, which forms part of the aza crown ether of 1, is concluded to be of crucial importance. It is shown that in solution a soft cation such as Ag+induces a greater special spectral shift than do hard cations of equal charge and almost the same size, such as Na+and K+. Solid‐state structures of the Ag+and Na+complexes of 1 show a relatively short Ag+‐N distance and a relatively long Na+‐ N distance.Netherlands Organization for Chemical Research (SON) with financial aid from the Netherlands Organization for Scientific Res

ISSN:0165-0513    

DOI:10.1002/recl.19901090304

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract(13–2H) 13‐Demethylretinal, (11,12,13‐2H,) 13‐demethylretinal, (9‐2H)9‐demethylretinal and (9,10‐2H2)9‐demethylretinal were prepared in all‐E, 9Z, 11Zand 13Zisomeric form with high deuterium incorporation. In the synthesis of (9,10‐2H2)9‐demethylretinal, a Horner‐Emmons reaction with deuteriated diethyl (cyanomethyl)phosphonate was used. This synthon was subsequently used for the synthesis of (10‐2H)‐ and (14‐2H)retinal in high yield and with high deuterium incorporation. From the13C NMR spectra of the demethylretinals (all‐E, 9Zand 13Z), he effect of a methyl group on the13CNMR parameters of polye

ISSN:0165-0513    

DOI:10.1002/recl.19901090305

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthetic usefulness of the deprotonation/protonation reaction of excited 1,2‐dihydronaphthalenes into 1,4‐dihydronaphthalenes induced by amines has been investigated using 13 different substituted 1,2‐dihydronaphthalenes and related compounds. The yield of the rearrangement ranges from 5 to 96%. The formation of side‐products depends on the position of protons in the substrate, which can be abstracted by the amine, and on competitive photore

ISSN:0165-0513    

DOI:10.1002/recl.19901090306

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe X‐ray excited emission spectra of gadolinium acetate tetrahydrate, [Gd ⊂ 2.2.1]Cl3·2H2O and Gd[C3F7COCHCOC(CH3)3]3(or Gd[FOD3), are reported. The first two compounds show strong Gd3+emission (6P←8S) at room temperature, while the third compound gives rise to strong ligand emission, but only at very low temperature. Eu(FOD)3, however, shows intense Eu3+emission upon X‐ray excitation. The Gd3+emission spectra show many vibronic lines and, although their intensity is weak, it is much higher than generally accepted. These vibronic lines indicate which groups coordinate the Gd3+ion and it is shown that their intensity increase as the ligand polarizability i

ISSN:0165-0513    

DOI:10.1002/recl.19901090307

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe high solubility of bismuth tribromide and bismuth trichloride in methyl methacrylate, propylene carbonate and other carbonyl‐containing compounds and polymers results from the interaction between bismuth and the carbonyl moiety. It was established by infrared,1H‐ and13C‐NMR measurements that in all these systems a 1:1 complex is formed. The bismuth trihalides are potentially useful as compatible X‐ray contrast additives for carbonyl‐containing

ISSN:0165-0513    

DOI:10.1002/recl.19901090308

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractElectrochemical oxidation of 2,4:3,5‐di‐O‐methylene‐D‐gluconic acid in strong alkaline medium afforded a mixture of 2,4:3,5‐di‐O‐methylene‐D‐glucaric acid4and 2,4:3,5‐di‐O‐methylene‐L‐idaric acid1in a 1/8 ratio with a current efficiency of 53%. Force‐field calculations using Allinger's molecular mechanics program MM2p85 on1and4indicate that thesecis‐fused tetrahydro‐[1,3]dioxino[5,4‐d]‐1,3‐dioxin ring systems possess an O‐inside conformation with a steric energy of 110.3 and 123.5 kJ·mol−1, respectively. Their conformation was confirmed by 400‐MHz1H‐ and 100‐MHz13C NMR measurements.A series of polycondensates were prepared by homogeneous solution polymerisation of1with an aromatic diol or

ISSN:0165-0513    

DOI:10.1002/recl.19901090309

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe short metal‐metal contacts frequently observed in solid indium(I) and thallium(I) cyclopentadienyls are interpreted as weak donor‐acceptor interactions, similar to the Sn‐Sn bond in dimeric stanny

ISSN:0165-0513    

DOI:10.1002/recl.19901090310

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe cycloaddition reaction of α‐oxo sulfines with 2‐(trimethylsiloxy)‐1,3‐dienes, leading ultimately to thiacyclohexanoneS‐oxides (alternatively named as thianoneS‐oxides or perhydrothiapyranoneS‐oxides) is described. 1‐Oxo‐2‐thioxo‐indaneS‐oxide2a, and several α‐oxo sulfines generatedin situhave been studied. The cycloaddition reaction is regioselective, and thiacyclohexan–3‐oneS‐oxides are the preponderant or the exclusive products. In the case of 1‐ethoxy‐3‐(tri‐methylsiloxy)‐1,3‐butadiene3cthe primary cycloadduct with sulfine2acan either undergo mild hydrolysis to give a thiacyclohexan‐3‐oneS‐oxide6hor elimination to give thia‐4‐cyclohexen‐3‐oneS‐oxide (2,6‐dihydrothiapyran‐3‐oneS‐oxide)6i. The regiochemistry of

ISSN:0165-0513    

DOI:10.1002/recl.19901090311

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY